Currently, a PN junction diode formed of Si is a mainstream of a photodiode to be used in an image sensor, and Si has an advantage in respect of leakage characteristics or easiness of fabrication. Meanwhile, in recent years, the refinement of a pixel progresses and there is a serious problem in that a noise deterioration is caused by a color mixture between adjacent pixels for an oblique incident light. In order to suppress the color mixture, it is necessary to thin the photodiode.
In the conventional photodiode formed of Si, however, it is necessary to ensure a thickness with a junction depth of approximately 3 μm to 4 μm in the photodiode in consideration of a penetration length of an absorption of a red light in a visible light region, particularly, on a long wavelength side. For this reason, it is hard to suppress the color mixture between the adjacent pixels with respect to the oblique incident light.